The invention relates to a coil for a melting pot with a ceramic-free outlet for the purpose of letting off a stream of molten metal. This coil is equipped with turns conducting electricity supplied by means of a feed line and a return line.
In the ceramic-free discharge of a stream of molten metal where the outlet that the melt flows through is formed by individual metal palisades that are surrounded by the coil, problems occur with known coil due to the high amount of power required to be introduced into the stream of melt since the shape of the coil and its current supply causes the power supply to be unsymmetrical and therefore inhomogeneous. This results in a deflection of the liquid stream of melt due to the magnetic fields of the coil. Such a deflection of the metal stream is undesirable in the case of subsequent further processing of the metal stream into powder or into a dead-mold casting or even prevents subsequent processes altogether.
Up to this point attempts were made to minimize the effect of a deflected stream of metal by using an additional compensating turn, by modifying the height between the turns of the coil or by changing the diameter of the coil locally. Furthermore, attempts have been made to locate bodies made from special magnetic alloys in the area of the outlet in order to compensate for such non-homogeneities in the magnetic field. The known processes, however, are always combined with a reduction of the effectiveness of the system and therefore do not solve the problem.
The invention is based on developing a coil of the previously mentioned type that allows for a high supply of power while maintaining a highly homogenous magnetic field.
The feed line and the return line are combined into one single current supply line in the area of the front side of the coil and this current supply line leads directly up to the turns. The turns run from that side of the coil that is located axially opposite to the current supply back to the return line in symmetrical arrangement to the turns leading to this front side.
Such a coil makes a coaxial current supply possible. Inside the turns of the coil, the current is distributed symmetrically due to the geometry of the semi-circular turn sections. This results in a magnetic field in the coil that is symmetrical to its center line which prevents a lateral deflection of the metal stream.
The coil as laid out by the invention can have several design variations. If the objective is to supply high levels of power into the liquid stream of metal without magnetic forces influencing the flow speed of the metal stream, the coil can be produced in a particularly cost-saving manner if the turns, coming from the feed line, initially form an almost semi-circular turn section, then a short connecting section running in the direction of the axis, after which another, almost semi-circular turn section with opposite direction of rotation (phase sequence) follows (FIG. 2).
Another condition is that the two axial connecting sections are connected by a turn circle that is almost a full circle on the side that is facing away from the current supply after a desired number of turn sections which are connected by the connecting sections that are oriented in axial direction and that the turn then runs toward the return line in symmetrical arrangement to the remaining turns.
If one intends to control the discharge of the metal in order to control the progression of a remelting process by means of magnetic forces that act upon on a metal stream, then a coil is beneficial which is distinguished by the fact that an almost semi-circular turn section is located adjacent to the power supply which is followed by a second, almost semi-circular turn section with the same orientation (phase sequence) that runs at a different height as a result of the oblique connecting section and if the turns run back to the return line after a desired number of turn sections from the far front side that is facing away from the power supply in symmetrical arrangement to the turns that lead to the opposite front side (FIG. 3).
A possible elliptic deformation of the metal stream due to the difference in height of the turn sections that are located opposite each other by 180.degree. can be minimized by providing, in accordance with another variation of the invention, a field weakening at the 90.degree. and 270.degree. positions respectively at the areas located between the two connecting sections. The remaining non-homogeneity of such a coil is located in the end area of the coil and does not have a negative effect there.
Another possibility of compensating non-homogeneities of the magnetic field is to vary the position and/or number of the palisades.
The invention allows for numerous variations. In order to explain it in more detail, two of these variations are illustrated in the diagram and will be described in the following.